[PATCH] D72733: [InstCombine] allow more narrowing of casted select

[Sanjay Patel via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rG747242af8dd0: [InstCombine] allow more narrowing of casted select (authored by spatel).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D72733/new/

https://reviews.llvm.org/D72733

Files:
  llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
  llvm/test/Transforms/InstCombine/cast-select.ll
  llvm/test/Transforms/InstCombine/select-imm-canon.ll
  llvm/test/Transforms/InstCombine/trunc.ll


Index: llvm/test/Transforms/InstCombine/trunc.ll
===================================================================
--- llvm/test/Transforms/InstCombine/trunc.ll
+++ llvm/test/Transforms/InstCombine/trunc.ll
@@ -626,15 +626,13 @@
   ret <2 x i8> %tr
 }
 
-; FIXME: If the select is narrowed based on the target's datalayout, we allow more optimizations.
+; If the select is narrowed based on the target's datalayout, we allow more optimizations.
 
 define i16 @PR44545(i32 %t0, i32 %data) {
 ; CHECK-LABEL: @PR44545(
-; CHECK-NEXT:    [[T1:%.*]] = add nuw nsw i32 [[T0:%.*]], 1
 ; CHECK-NEXT:    [[ISZERO:%.*]] = icmp eq i32 [[DATA:%.*]], 0
-; CHECK-NEXT:    [[FFS:%.*]] = select i1 [[ISZERO]], i32 0, i32 [[T1]]
-; CHECK-NEXT:    [[CAST:%.*]] = trunc i32 [[FFS]] to i16
-; CHECK-NEXT:    [[SUB:%.*]] = add nsw i16 [[CAST]], -1
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 [[T0:%.*]] to i16
+; CHECK-NEXT:    [[SUB:%.*]] = select i1 [[ISZERO]], i16 -1, i16 [[TMP1]]
 ; CHECK-NEXT:    ret i16 [[SUB]]
 ;
   %t1 = add nuw nsw i32 %t0, 1
Index: llvm/test/Transforms/InstCombine/select-imm-canon.ll
===================================================================
--- llvm/test/Transforms/InstCombine/select-imm-canon.ll
+++ llvm/test/Transforms/InstCombine/select-imm-canon.ll
@@ -39,8 +39,8 @@
 ; CHECK-LABEL: @thisdoesnotloop(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[L1:%.*]] = icmp slt i32 [[A:%.*]], -128
-; CHECK-NEXT:    [[L2:%.*]] = select i1 [[L1]], i32 -128, i32 [[B:%.*]]
-; CHECK-NEXT:    [[CONV7:%.*]] = trunc i32 [[L2]] to i8
+; CHECK-NEXT:    [[TMP0:%.*]] = trunc i32 [[B:%.*]] to i8
+; CHECK-NEXT:    [[CONV7:%.*]] = select i1 [[L1]], i8 -128, i8 [[TMP0]]
 ; CHECK-NEXT:    ret i8 [[CONV7]]
 ;
 entry:
Index: llvm/test/Transforms/InstCombine/cast-select.ll
===================================================================
--- llvm/test/Transforms/InstCombine/cast-select.ll
+++ llvm/test/Transforms/InstCombine/cast-select.ll
@@ -56,8 +56,8 @@
 define i16 @trunc(i32 %x, i32 %y, i32 %z) {
 ; CHECK-LABEL: @trunc(
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[SEL:%.*]] = select i1 [[CMP]], i32 42, i32 [[Z:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = trunc i32 [[SEL]] to i16
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 [[Z:%.*]] to i16
+; CHECK-NEXT:    [[R:%.*]] = select i1 [[CMP]], i16 42, i16 [[TMP1]]
 ; CHECK-NEXT:    ret i16 [[R]]
 ;
   %cmp = icmp ult i32 %x, %y
Index: llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -276,16 +276,20 @@
   }
 
   if (auto *Sel = dyn_cast<SelectInst>(Src)) {
-    // We are casting a select. Try to fold the cast into the select, but only
-    // if the select does not have a compare instruction with matching operand
-    // types. Creating a select with operands that are different sizes than its
+    // We are casting a select. Try to fold the cast into the select if the
+    // select does not have a compare instruction with matching operand types
+    // or the select is likely better done in a narrow type.
+    // Creating a select with operands that are different sizes than its
     // condition may inhibit other folds and lead to worse codegen.
     auto *Cmp = dyn_cast<CmpInst>(Sel->getCondition());
-    if (!Cmp || Cmp->getOperand(0)->getType() != Sel->getType())
+    if (!Cmp || Cmp->getOperand(0)->getType() != Sel->getType() ||
+        (CI.getOpcode() == Instruction::Trunc &&
+         shouldChangeType(CI.getSrcTy(), CI.getType()))) {
       if (Instruction *NV = FoldOpIntoSelect(CI, Sel)) {
         replaceAllDbgUsesWith(*Sel, *NV, CI, DT);
         return NV;
       }
+    }
   }
 
   // If we are casting a PHI, then fold the cast into the PHI.


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